Field of the Invention PA1 Description of the Prior Art
The present invention relates to an electromagnetic relay, more specifically to an electromagnetic relay of the size of, for example, 20 mm .times.10 mm .times.15 mm.
An example of a prior art electromagnetic relay is described with reference to FIG. 1, which is one of the drawings indicated in the "brief description of the drawings" set forth later. The electromagnetic relay of FIG. 1 comprises bobbin 110, coil 120, pole piece 152, yoke 153, armature 140 of a bent bar shape, hinge spring 141, card 160, movable contact springs 31m (make-contact side) and 31b (break-contact side), fixed contact spring 210, restoring spring 4, insulators 51, 52, 53, 54, and 55, stop metal 7, connection screw 6, and pressure screw 8. The electromagnet structure (110, 120, 152, 153, 140), hinge spring 141, and the spring structure (31m, 31b, 210, 4, 51, 52, 53, 54, 55, 7, 8) are combined as an electromagnetic relay assembly by using connection screw 6. Card 160 is arranged between armature 140 and movable contact springs 31m, 31b.
In the electromagnetic relay of FIG. 1, there are problems in realizing the precise positional relationships between the various elements of the electromagnetic relay and ensuring the sensitive and uniform operation of the electromagnetic relay by relatively low electric power. This is mainly because the error in the positions of the elements of the electromagnetic relay cannot be reduced to below a predetermined level due to the accumulation of positional errors of the plurality of the movable and fixed contact springs and the hinge spring. Hence, it is difficult to keep the distance between the driving edge of the card and the surface of the movable contact within a predetermined allowable value.
Also, in the electromagnetic relay of FIG. 1, the variation of the distance between one end 140a of armature 140 and pole piece 152 causes greater variation of the stroke of the other end 140b of armature 140 due to the so-called "lever ratio" of armature 140. Also, it is not easy to manufacture such a bent bar shape armature with high precision. Thus, it is generally difficult to ensure the sensitive and uniform operation of the electromagnetic relay by relatively low electric power.